1. Field of the Invention
This invention relates to the field of inductors for use in electrical circuits. More particularly, it relates to an improved inductor structure for use at relatively high frequencies as an output inductor for an inverter power supply.
2. State of the Prior Art
In power supply design, it is often required that power supplies be provided that will give voltages in a range of values. For example, output voltages of 2volts, 5 volts, and 12 volts are common power supply voltages for use in conjunction with electronic circuitry. One type of power supply in usage involves inverter circuits driving a transformer from a source of input signals, with the secondary of the transformer being utilized to drive a rectifier circuit. The output of the rectifier circuit is commonly applied through output inductors to provide power to circuitry. The inverter circuits are functioning in ranges of 200 kHz and above in the power supply environment. These frequencies and the circuit environment require that the inductors have a low self-capacitance.
The packaging of electronic circuitry and associated power supplies often utilizes printed circuit boards for making circuit interconnection. As the electronic circuitry gets ever-smaller the overall packaging becomes more dense, and it is necessary that associated components become smaller. It is desireable therefore that an inductor for use in the modern day power supplies have a low profile, be compatible with installation in printed circuit board assemblies, be inexpensive, and be adaptable for different power supply requirements.
The prior art has many examples of inductors designed for uses in many applications. At one extreme in size consideration the prior art illustrates a solid-state inductor constructed from multiple thin film layers in U.S. Pat. No. 3,210,707 to Constantakes. This structure is relatively expensive to fabricate and does not have power capabilities or selective turns capability of the subject invention. A relatively large inductor is shown in the D-core structure of U.S. Pat. No. 3,238,484 to Dacey, where windings are wound on the C portion of the core. Others have found improvement to inductors by special composition of the core material, for example shown in U.S. Pat. No. 4,183,079 to Wachi. A specialized structure utilizing segments of ferromagnetic material and associated windings is shown in U.S. Pat. No. 4,183,783 to Portier, and a specialized method of fabrication of ferrite cores for use in a microwave device is shown in U.S. Pat. No. 4,007,541 to Monforte et al.
An inductance fabricated in conjunction with a metal printed circuit board is shown in U.S. Pat. No. 4,201,965 to Onyshkevych. The device taught therein utilizes a metalic supporting board with associated insulating layers, and core material mounted through holes therein. Associated windings are formed in layers of printed circuit foil in spiral configuration around the holes that are utilized to receive the core. None of the discovered prior art illustrates or suggests the structure of the invention.